This invention relates to a new method of preparing crystalline molecular sieve compositions.
Zeolitic materials, both natural and synthetic, are known to have catalytic capabilities for many hydrocarbon processes. Zeolitic materials typically are ordered porous crystalline aluminosilicates having a definite structure with cavities interconnected by channels. The cavities and channels throughout the crystalline material generally are uniform in size allowing selective separation of hydrocarbons. Consequently, these materials in many instances are known in the art as "molecular sieves" and are used, in addition to selective adsorptive processes, for certain catalytic properties. The catalytic properties of these materials are affected to some extent by the size of the molecules which selectively penetrate the crystal structure, presumably to contact active catalytic sites within the ordered structure of these materials.
Generally, the term "molecular sieve" includes a wide variety of both natural and synthetic cation-containing crystalline zeolite materials. They generally are characterized as crystalline aluminosilicates which comprises networks of SiO.sub.4 and AlO.sub.4 tetrahedra in which silicon and aluminum atoms are cross-linked by sharing of oxygen atoms. The negative framework charge resulting from the substitution of an aluminum atom for a silicon atom is balanced by cations, for example, alkali-metal or alkaline-earth-metal cations, ammonium ions, or hydrogen ions.
Prior art developments have resulted in the formations of many synthetic zeolitic crystalline materials. Crystalline aluminosilicates are the most prevalent and, as described in the patent literature and in the published journals, are designated by letters or other convenient symbols. Examples of these materials are Zeolite A (U.S. Pat. No. 2,882,243), Zeolite X (U.S. Pat. No. 2,882,244), Zeolite Y (U.S. Pat. No. 3,130,007), Zeolite ZSM-4 (U.S. Pat. No. 3,578,723), Zeolite ZSM-5 (U.S. Pat. No. 3,702,886), Zeolite ZSM-11 (U.S. Pat. No. 3,709,979), Zeolite ZSM-12 (U.S. Pat. No. 3,832,449), Zeolite NU-1 (U.S. Pat. No. 4,060,590) and others.
Molecular sieves characterized as "ferrierite" by a combination of chemical composition and X-ray diffraction spectra are known as naturally occurring materials and as synthesized materials. For example, a conventional ferrierite sieve is produced by crystallizing a basic mixture of sodium aluminate and an oxide of silicon without the use of an organic template compound. Such ferrierites are described in D. W. Breck "Zeolite Molecular Sieves," John Wiley & Sons, 1974, incorporated by reference herein. U.S. Pat. No. 4,000,248 discloses a method of producing a ferrierite molecular sieve using N-methyl pyridinium hydroxide as an organic template compound in the crystallization of the sieve. U.S. Pat. Nos. 4,016,245, 4,107,195 and 4,046,859 disclose formation of a ferrierite-like material using an organic template derived from ethylenediamine, pyrrolidine or butanediamine or organometallic 2-(hydroxyalkyl)trialkylaluminum compounds. The present invention is a new method of preparing a ferrierite molecular sieve using simple organic compounds as templates in which silicon/aluminum (Si/Al) ratio (or as expressed as oxides, the silica/alumina (SiO.sub.2 /Al.sub.2 O.sub.3) ratio) can be adjusted to effect better selectivity in hydrocarbon conversion reactions.